Liquid crystal medium and liquid crystal display

ABSTRACT

The instant invention relates to mesogenic media comprising one or more compounds selected from the group of compounds of formulae M-I and M-II 
                         
wherein the parameters are as specified in the text, preferably to mesogenic media showing a blue phase, preferably stabilized by a polymer, and their use in electro-optical light modulation elements and their respective use in displays, as well as to such devices.

FIELD OF THE INVENTION

The present invention relates to compounds, media comprising thesecompounds and to electro-optical displays comprising these media aslight modulation media. Preferably the compounds of the presentinvention are mesogenic compounds and they are preferably used in liquidcrystalline media. In particular the electro-optical displays accordingto the present invention are displays, which are operated at atemperature, at which the mesogenic modulation media are in an opticallyisotropic phase, preferably in a blue phase.

PROBLEM TO BE SOLVED AND STATE OF THE ART

Electro-optical displays and mesogenic light modulation media, which arein the isotropic phase when being operated in the display are describedin DE 102 17 273 A. Electro-optical displays, and mesogenic lightmodulation media, which are in the optically isotropic blue phase, whenbeing operated in the display are described in WO 2004/046 805.

is e.g. mentioned in EP 1 006 109 A1.Compounds of the formula

are e.g. proposed for liquid crystalline media for IPS displays in WO2008/128623 A1.EP 2 302 015 A1 shows the use of

as well as of

in a simple nematic host mixture and the use of

in a dielectrically positive liquid crystal mixture, comprising thechiral compound

which exhibits a blue phase and is stabilized by photo-polymerization ofa reactive mesogen of the formula

WO 2010/058681 A1 mentions, amongst other compounds,

which exhibit a nematic phase, and also optically isotropic liquidcrystalline media comprising these compounds besides other compoundssuch as e.g.

U.S. Pat. No. 7,070,838 describes polymerisable compounds containing a2-di- or trifluoromethyl-1,4-phenyl ring, and the use thereof inpolymerisable mixtures, LC polymers and LC displays having a cholestericphase and in optical films. Specific compounds of a formula 1a-2-19having the following structure are also disclosed therein

However, no properties of this compound on use in an LC display aredisclosed. In addition, the use of such compounds for the stabilisationof blue phases or in PSA displays is neither described in nor is obviousfrom U.S. Pat. No. 7,070,838.

JP 2005-015473 A discloses polymerisable compounds containingunsaturated spacer groups (alkynylene or alkenylene). Specific compoundsof the formulae 1-13-77 to 1-13-84, 1-13-134, 1-13-135, 1-56-9, 1-56-10,1-56-23, 1-56-24 which contain phenyl rings linked via CF₂O bridges arealso disclosed therein, as is the use thereof for the production ofoptically anisotropic films and in ferroelectric LC media. Specificcompounds, for example having the following structures, are alsodisclosed therein.

However, the use of such compounds for the stabilisation of blue phasesor in PSA displays is neither described in nor is obvious from JP2005-015473 A.

The specifications US 2009/0268143 and US 2010/0078593 claimdifluorooxymethylene-bridged polymerisable compounds containing a ringsystem having negative dielectric anisotropy as a component inliquid-crystal mixtures for anisotropic films.

However, no properties of these compounds on use in an LC display aredisclosed. In addition, the use of such compounds for the stabilisationof blue phases or in PSA displays is neither described in nor is obviousfrom these specifications.

The mesogenic media and displays described in these references provideseveral significant advantages compared to well-known and widely useddisplays using liquid crystals in the nematic phase, like for exampleliquid crystal displays (LCDs) operating in the twisted nematic (TN)-,the super twisted nematic (STN)-, the electrically controlledbirefringence (ECB)-mode with its various modifications and the in-planeswitching (IPS)-mode.

Amongst these advantages are most pronounced their much faster switchingtimes, and significantly wider optical viewing angle.

Whereas, compared to displays using mesogenic media in another liquidcrystalline phase, as e.g. in the smectic phase in surface stabilizedferroelectric liquid crystal displays (SSF LCDs), the displays of DE 10217 273.0 and WO 2004/046 805 are much easier to manufacture. Forexample, they do not require a very thin cell gap and in addition theelectro-optical effect is not very sensitive to small variations of thecell gap.

However, the liquid crystal media described in these patent applicationsmentioned still require operating voltages, which are not low enough forsome applications. Further the operating voltages of these media varywith temperature, and it is generally observed, that at a certaintemperature the voltage dramatically increases with increasingtemperature. This limits the applicability of liquid crystal media inthe blue phase for display applications. A further disadvantage of theliquid crystal media described in these patent applications is theirmoderate reliability which is insufficient for very demandingapplications. This moderate reliability may be for example expressed interms of the voltage holding ratio (VHR) parameter, which in liquidcrystal media as described above may be below 90%.

Some compounds and compositions have been reported which possess a bluephase between the cholesteric phase and the isotropic phase and canusually be observed by optical microscopy. These compounds orcompositions for which the blue phases are observed are typically singlemesogenic compounds or mixtures showing a high chirality. However,generally the blue phases observed only extend over a very smalltemperature range, which is typically less than 1 degree centigradewide, and/or the blue phase is located at rather inconvenienttemperatures.

In order to operate the novel fast switching display mode of WO 2004/046805 the light modulation medium to be used has to be in the blue phaseover a broad range of temperatures encompassing ambient temperature,however. Thus, a light modulation medium possessing a blue phase, whichis as wide as possible and conveniently located is required.

Therefore there is a strong need for a modulation medium with a bluephase with a wide phase range, which may be achieved either by anappropriate mixture of mesogenic compounds themselves or, preferably bymixing a host mixture with appropriate mesogenic properties with asingle dopant or a mixture of dopants that stabilises the blue phaseover a wide temperature range.

Summarizing, there is a need for liquid crystal media, which can beoperated in liquid crystal displays, which are operated at temperatureswhere the media is in the blue phase, which provide the followingtechnical improvements:

-   -   a reduced operating voltage,    -   a reduced temperature dependency of the operating voltage and    -   an improved reliability, e.g. VHR.

Present Invention

Surprisingly, it now has been found that mesogenic media exhibiting ablue phase and comprising one or more compounds selected from the groupof compounds of formulae M-I and M-II

-   -   wherein    -   L⁰ is H or F, preferably F,    -   R⁰ is alkyl, which is straight chain or branched, is        unsubstituted, mono- or poly-substituted by F, Cl or CN,        preferably by F, and in which one or more CH₂ groups are        optionally replaced, in each case independently from one        another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—,        —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such a manner        that O and/or S atoms are not linked directly to one another,    -   Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN, and        alternatively one of them may be H,    -   R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1        to 12 C-atoms,    -   amongst which chiral compounds are encompassed, too, allow to        realize media with an acceptably high clearing point and/or a        rather high stability of the voltage holding ratio against        temperature and/or UV-load and in particular against the latter.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula M-I, preferably selected from thegroup of compounds of its sub-formulae M-I-1 and M-I-2, preferably offormula M-I-2,

wherein R⁰ has the meaning given under formula M-I above and preferablyis n-alkyl, most preferably ethyl, n-propyl, n-butyl, n-pentyl orn-hexyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula M-I-1, preferably selected fromthe group of compounds of its sub-formulae M-I-1a to M-I-1c, preferablyof formulae M-I-1a and/or M-I-1b, preferably of formula M-I-1b,

wherein R⁰ has the meaning given under formula M-I-1 above andpreferably is n-alkyl, most preferably ethyl, n-propyl, n-butyl,n-pentyl or n-hexyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula M-I-2, preferably selected fromthe group of compounds of its sub-formulae M-I-2a to M-I-2c, preferablyof formulae M-I-2a and/or M-I-2b, preferably of formula M-I-2b,

wherein R⁰ has the meaning given under formula M-I-2 above.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula M-II, preferably selected fromthe group of compounds of its sub-formulae M-II-1 and M-II-2, preferablyof formula M-II-2,

wherein R⁰ has the meaning given under formula M-II above and preferablyis n-alkyl, most preferably ethyl, n-propyl, n-butyl, n-pentyl orn-hexyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula M-II-1, preferably selected fromthe group of compounds of its sub-formulae M-II-1a to M-II-1c,preferably of formulae M-II-1a and/or M-II-1b, preferably of formulaM-II-1b,

wherein R⁰ has the meaning given under formula M-II-1 above.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula M-II-2, preferably selected fromthe group of compounds of its sub-formulae M-II-2a to M-II-2c,preferably of formulae M-II-2a and/or M-II-2b, preferably of formulaM-II-2b,

wherein R⁰ has the meaning given under formula M-II-2 above.

It has been further been found that mesogenic media, which arecomprising, additionally to the compound or the compounds of formulaeM-1 and/or M-II, or of their respective preferred sub-formulae, one ormore compounds selected from the group of compounds of formulae I and II

wherein

-   L¹ is H or F, preferably F,-   L²¹ to L²³ are, independently of each other, H or F, preferably L²¹    and L²² are both F and/or L²³ is F,-   R¹ and R² are, independently of each other, alkyl, which is straight    chain or branched, preferably has 1 to 20 C-atoms, is unsubstituted,    mono- or poly-substituted by F, Cl or CN, preferably by F, and in    which one or more CH₂ groups are optionally replaced, in each case    independently from one another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—,    —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in    such a manner that O and/or S atoms are not linked directly to one    another, preferably n-alkyl, n-alkoxy with 1 to 9 C-atoms,    preferably 2 to 5 C-atoms, alkenyl, alkenyloxy or alkoxyalkyl with 2    to 9 C-atoms, preferably with 2 to 5 C-atoms or halogenated alkyl,    halogenated alkenyl or halogenated alkoxy, preferably mono    fluorinated, di-fluorinated or oligofluorinated alkyl, alkenyl or    alkoxy, most preferably n-alkyl, n-alkoxy, alkenyl, alkenyloxy or    alkoxyalkyl,-   Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN, and    alternatively one of them may be H,-   R⁰¹ and R⁰² are, independently of each other, H or alkyl with 1 to    12 C-atoms,    amongst which chiral compounds are encompassed, too, allow to    realize media with an acceptably high clearing point and/or a rather    high stability of the voltage holding ratio against temperature    and/or UV-load and in particular against the latter.

In a preferred embodiment of the present invention the media accordingto the present invention additionally comprise one more compounds offormula III

wherein

-   R³ has one of the meanings given for R¹ under formula I above.

Preferably the media according to the present invention additionallycomprise one more compounds selected from the group of compounds offormulae IV and V

wherein

-   R⁴ and R⁵ are, independently of each other, alkyl, which is straight    chain or branched, preferably has 1 to 20 C-atoms, is unsubstituted,    mono- or poly-substituted by F, Cl or CN, preferably by F, and in    which one or more CH₂ groups are optionally replaced, in each case    independently from one another, by —O—, —S—, —CO—, —COO—, —OCO—,    —OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a manner that O and/or S    atoms are not linked directly to one another, preferably n-alkyl,    n-alkoxy with 1 to 9 C-atoms, preferably 2 to 5 C-atoms, alkenyl,    alkenyloxy or alkoxyalkyl with 2 to 9 C-atoms, preferably with 2 to    5 C-atoms, most preferably n-alkyl, n-alkoxy, alkenyl, alkenyloxy or    alkoxyalkyl,-   L⁵ is H or F, preferably F,

and

-   n and m are, independently of one another, 0 or 1, preferably m is    1.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula I, preferably selected from thegroup of compounds of its sub-formulae I-1 and I-2, preferably offormula I-2,

wherein R¹ has the meaning given under formula I above and preferably isn-alkyl, most preferably ethyl, n-propyl, n-butyl, n-pentyl or n-hexyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula II, preferably a compound whereinR² has the meaning given under formula II above and more preferably isn-alkyl, more preferably ethyl, n-propyl, n-butyl, n-pentyl or n-hexyland, most preferably n-butyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula II, preferably selected from thegroup of compounds of its sub-formulae II-1 to II-8, preferably offormula II-1 to II-4, most preferably of formula II-3,

wherein R² has the meaning given under formula II above and preferablyis n-butyl or n-pentyl.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula IV, preferably selected from thegroup of compounds of its sub-formulae IV-1 to IV-4, preferably offormula IV-2,

wherein R⁴ has the meaning given under formula IV above.

In a preferred embodiment of the present invention the mesogenic mediacomprise one more compounds of formula V, preferably selected from thegroup of compounds of its sub-formulae V-1 and V-2, preferably one ormore compounds of formula V-1 and one or more compounds of formula V-2,

wherein R⁵ has the meaning given under formula V above.

An alkyl or an alkoxy radical, i.e. an alkyl where the terminal CH₂group is replaced by —O—, in this application may be straight-chain orbranched. It is preferably straight-chain, has 1, 2, 3, 4, 5, 6, 7 or 8carbon atoms and accordingly is preferably methyl, ethyl, propyl, butyl,pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy,heptoxy, or octoxy, furthermore nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy,tridecoxy or tetradecoxy, for example.

Oxaalkyl, i.e. an alkyl group in which one non-terminal CH₂ group isreplaced by —O—, is preferably straight-chain 2-oxapropyl(=methoxy-methyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl),2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or 5-oxahexyl, 2-, 3-, 4-, 5-, or6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl, for example.

An alkenyl group, i.e. an alkyl group wherein one or more CH₂ groups arereplaced by —CH═CH—, may be straight-chain or branched. It is preferablystraight-chain, has 2 to 10 C atoms and accordingly is preferably vinyl,prop-1-, or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- orpent-4-enyl, hex-1-, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5-or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-,3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- ordec-9-enyl.

Especially preferred alkenyl groups are C₂-C₇-1E-alkenyl,C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, inparticular C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl.Examples for particularly preferred alkenyl groups are vinyl,1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl,3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl,4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groupshaving up to 5 C-atoms are generally preferred.

In an alkyl group, wherein one CH₂ group is replaced by —O— and one by—CO—, these radicals are preferably neighboured. Accordingly theseradicals together form a carbonyloxy group —CO—O— or an oxycarbonylgroup —O—CO—. Preferably such an alkyl group is straight-chain and has 2to 6 C atoms.

It is accordingly preferably acetyloxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl,2-propionyloxy-ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl,3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxy-carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl, 4-(methoxycarbonyl)-butyl.

An alkyl group wherein two or more CH₂ groups are replaced by —O— and/or—COO—, it can be straight-chain or branched. It is preferablystraight-chain and has 3 to 12 C atoms. Accordingly it is preferablybis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl,4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6,6-bis-carboxy-hexyl,7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl,10,10-bis-carboxy-decyl, bis-(methoxycarbonyl)-methyl,2,2-bis-(methoxycarbonyl)-ethyl, 3,3-bis-(methoxycarbonyl)-propyl,4,4-bis-(methoxycarbonyl)-butyl, 5,5-bis-(methoxycarbonyl)-pentyl,6,6-bis-(methoxycarbonyl)-hexyl, 7,7-bis-(methoxycarbonyl)-heptyl,8,8-bis-(methoxycarbonyl)-octyl, bis-(ethoxycarbonyl)-methyl,2,2-bis-(ethoxycarbonyl)-ethyl, 3,3-bis-(ethoxycarbonyl)-propyl,4,4-bis-(ethoxycarbonyl)-butyl, 5,5-bis-(ethoxycarbonyl)-hexyl.

A alkyl or alkenyl group that is monosubstituted by CN or CF₃ ispreferably straight-chain. The substitution by CN or CF₃ can be in anydesired position.

An alkyl or alkenyl group that is at least monosubstituted by halogen,it is preferably straight-chain. Halogen is preferably F or Cl, in caseof multiple substitution preferably F. The resulting groups include alsoperfluorinated groups. In case of monosubstitution the F or Clsubstituent can be in any desired position, but is preferably inω-position. Examples for especially preferred straight-chain groups witha terminal F substituent are fluoromethyl, 2-fluoroethyl,3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and7-fluoroheptyl. Other positions of F are, however, not excluded.

Halogen means F, Cl, Br and I and is preferably F or Cl, most preferablyF. Each of R¹, R⁵, R, R′ and R″ may be a polar or a non-polar group. Incase of a polar group, it is preferably selected from CN, SF₅, halogen,OCH₃, SCN, COR⁵, COOR⁵ or a mono-oligo- or polyfluorinated alkyl oralkoxy group with 1 to 4 C atoms. R⁵ is optionally fluorinated alkylwith 1 to 4, preferably 1 to 3 C atoms. Especially preferred polargroups are selected of F, Cl, CN, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅,CF₃, CHF₂, CH₂F, OCF₃, OCHF₂, OCH₂F, C₂F₅ and OC₂F₅, in particular F,Cl, CN, CF₃, OCHF₂ and OCF₃. In case of a non-polar group, it ispreferably alkyl with up to 15 C atoms or alkoxy with 2 to 15 C atoms.

Each of R¹ to R⁵ may be an achiral or a chiral group. In case of achiral group it is preferably of formula I*:

wherein

-   Q¹ is an alkylene or alkylene-oxy group with 1 to 9 C atoms or a    single bond,-   Q² is an alkyl or alkoxy group with 1 to 10 C atoms which may be    unsubstituted, mono- or polysubstituted by F, Cl, Br or CN, it being    also possible for one or more non-adjacent CH₂ groups to be    replaced, in each case independently from one another, by —C≡C—,    —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO— or    —CO—S— in such a manner that oxygen atoms are not linked directly to    one another,-   Q³ is F, Cl, Br, CN or an alkyl or alkoxy group as defined for Q²    but being different from Q².

In case Q¹ in formula I* is an alkylene-oxy group, the O atom ispreferably adjacent to the chiral C atom.

Preferred chiral groups of formula I* are 2-alkyl, 2-alkoxy,2-methylalkyl, 2-methylalkoxy, 2-fluoroalkyl, 2-fluoroalkoxy,2-(2-ethin)-alkyl, 2-(2-ethin)-alkoxy, 1,1,1-trifluoro-2-alkyl and1,1,1-trifluoro-2-alkoxy.

Particularly preferred chiral groups I* are 2-butyl (=1-methylpropyl),2-methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, in particular 2-methylbutyl, 2-methylbutoxy,2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy,2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl,2-hexyl, 2-octyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy,6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl,2-methylbutyryloxy, 3-methylvaleroyloxy, 4-methylhexanoyloxy,2-chlorpropionyloxy, 2-chloro-3-methylbutyryloxy,2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy,2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1-methoxypropyl-2-oxy,1-ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy, 1-butoxypropyl-2-oxy,2-fluorooctyloxy, 2-fluorodecyloxy, 1,1,1-trifluoro-2-octyloxy,1,1,1-trifluoro-2-octyl, 2-fluoromethyloctyloxy for example. Verypreferred are 2-hexyl, 2-octyl, 2-octyloxy, 1,1,1-trifluoro-2-hexyl,1,1,1-trifluoro-2-octyl and 1,1,1-trifluoro-2-octyloxy.

In addition, compounds containing an achiral branched alkyl group mayoccasionally be of importance, for example, due to a reduction in thetendency towards crystallization. Branched groups of this type generallydo not contain more than one chain branch. Preferred achiral branchedgroups are isopropyl, isobutyl (=methylpropyl), isopentyl(=3-methylbutyl), isopropoxy, 2-methyl-propoxy and 3-methylbutoxy.

Preferably the liquid crystalline media according to the presentinvention comprise one or more reactive compounds, respectivelypolymerisable compounds, each comprising one, two ore more reactivegroups, respectively polymerizable groups. This is obvious, as themesogenic material preferably is stabilized in the blue phase by theformation of a polymer, which may have the form of a matrix or of anetwork.

For use in a display application, the temperature range of typicalmaterials, which are exhibiting a pure blue phase (BP) on their own,generally is not wide enough. Such materially typically have a bluephase, which extends over a small temperature range of only somedegrees, e.g. about 3 to 4°. Thus, an additional stabilisation,extending the temperature range of the blue phase, is needed in order tomake such material suitable for practical applications such as indisplays.

In order to stabilise the blue phase by the formation of a polymer, theformulated blue phase host mixture is conveniently combined with anappropriate chiral dopant (one or more suitable chiral compounds) andwith one or more reactive compounds, preferably reactive mesogeniccompounds (RMs). The resultant mixture is filled into the LC cellrespectively display panel. The LC cell/panel is then held at a certaintemperature at which the mixture is in the blue phase, e.g. it is heatedor cooled until blue phase can be observed at a certain temperature.This temperature is maintained during the whole polymerisation process.The polymerisation process is typically controlled by UV irradiation ofa typical medium-pressure mercury-vapour lamp. A standard condition ise.g. use of 3 mW/cm² for 180 sec. at a wavelength of 380 nm. To avoiddamage to the LC material appropriate optical filters can be usedadditionally.

In the following the criteria for stability of the obtained polymerstabilised blue phase (BP) are briefly be explained.

Ensuring an excellent quality of the polymer stabilisation is criticalfor use of PS-BP in a display application. The quality of polymerstabilization is the judged by several criteria. Optical inspectionensures a good polymerisation. Any defect and/or haziness observed inthe test cell/panel is an indication of an suboptimal polymerstabilisation. Electro-optical inspection under various load/stressconditions ensures long-time stability of the PS-BP. A typical displayparameter is the so-called memory effect (ME). The memory effect isdefined as the ratio of the contrast ratio for switching on and of thecontrast ratio for switching off as a normalized measure of the residualtransmission after one or more switching cycles have been executed. Avalue for this memory effect of 1.0 is an indicator of an excellentpolymer stabilisation. A value for this memory effect of more than 1.1indicates insufficient stabilisation of the blue phase.

The present invention further relates to an LC medium comprising one ormore compounds selected from the group of the compounds of the formulaeI and II and optionally III, a chiral dopant and one or more compoundsof the formula PP^(a)-(Sp^(a))_(s1)-(A¹-Z¹)_(n1)-A²-Q-A³-(Z⁴-A⁴)_(n2)-(Sp^(b))_(s2)-P^(b)  Pwherein the individual radicals have the following meanings:

-   P^(a), P^(b) each, independently of one another, are a polymerisable    group,-   Sp^(a), Sp^(b) each, independently of one another, denote a spacer    group,-   s1, s2 each, independently of one another, denote 0 or 1,-   n1, n2 each, independently of one another, denote 0 or 1, preferably    0,-   Q¹ denotes —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —(CO)O—, —O(CO)—,    —(CH₂)₄—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—, —CH₂—CF₂—, —CH═CH—,    —CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CF—, —C≡C—, —O—, —CH₂—,    —(CH₂)₃—, —CF₂—, preferably —CF₂O—,-   Z⁶¹, Z⁶²-   Z¹, Z⁴ denote a single bond, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,    —(CO)O—, —O(CO)—, —(CH₂)₄—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—,    —CH₂—CF₂—, —CH═CH—, —CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃, —CH═CF—,    —C≡C—, —O—, —CH₂—, —(CH₂)₃—, —CF₂—, where Z¹ and Q¹ or Z² and Q¹ do    not simultaneously denote a group selected from —CF₂O— and —OCF₂—,-   A¹, A², A³, A⁴    -   each, independently of one another, denote a radical selected        from the following groups:    -   a) the group consisting of trans-1,4-cyclohexylene,        1,4-cyclohexenylene and 1,4′-bicyclohexylene, in which, in        addition, one or more non-adjacent CH₂ groups may be replaced by        —O— and/or —S— and in which, in addition, one or more H atoms        may be replaced by F,    -   b) the group consisting of 1,4-phenylene and 1,3-phenylene, in        which, in addition, one or two CH groups may be replaced by N        and in which, in addition, one or more H atoms may be replaced        by L,    -   c) the group consisting of tetrahydropyran-2,5-diyl,        1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl,        cyclobutane-1,3-diyl, piperidine-1,4-diyl, thiophene-2,5-diyl        and selenophene-2,5-diyl, each of which may also be mono- or        polysubstituted by L,    -   d) the group consisting of saturated, partially unsaturated or        fully unsaturated, and optionally substituted, polycyclic        radicals having 5 to 20 cyclic C atoms, one or more of which        may, in addition, be replaced by heteroatoms, preferably        selected from the group consisting of        bicyclo[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl,        spiro[3.3]heptane-2,6-diyl,

-   -    where, in addition, one or more H atoms in these radicals may        be replaced by L, and/or one or more double bonds may be        replaced by single bonds, and/or one or more CH groups may be        replaced by N,

-   L on each occurrence, identically or differently, denotes F, Cl, CN,    SCN, SF₅ or straight-chain or branched, in each case optionally    fluorinated, alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl,    alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms,

-   R⁰, R⁰⁰ each, independently of one another, denote H, F or    straight-chain or branched alkyl having 1 to 12 C atoms, in which,    in addition, one or more H atoms may be replaced by F,

-   M denotes —O—, —S—, —CH₂—, —CHY¹— or —CY¹Y²—, and

-   Y¹ and Y² each, independently of one another, have one of the    meanings indicated above for R⁰, or denote Cl or CN, and one of the    groups Y¹ and Y² alternatively denotes —OCF₃, preferably H, F, Cl,    CN or CF₃,    as well as to a polymer stabilized system obtainable by    polymerisation of one or more compounds of the formula P alone or in    combination with on or more further polymerisable compounds from a    respective mixture, and to the use of such a stabilized system in    electro-optical displays having a blue phase.

Compounds of the formula P used preferably according to the presentinvention are selected from the group consisting of the followingformulae:

in which L in each occurrence, identically or differently, has one ofthe meanings indicated above and below, r denotes 0, 1, 2, 3 or 4, sdenotes 0, 1, 2 or 3, and n denotes an integer between 1 and 24,preferably between 1 and 12, very particularly preferably between 2 and8, and in which, if a radical is not indicated at the end of a single ordouble bond, it is a terminal CH₃ or CH₂ group.

In the formulae P1 to P24,

preferably denotes a group selected from the group consisting of thefollowing formulae:

particularly preferably

The group A²-Q-A³ preferably denotes a group of the formula

in which at least one of the rings is substituted by at least one groupL=F. r here is in each case, independently, preferably 0, 1 or 2.

P^(a) and P^(b) in the compounds of the formula P and the sub-formulaethereof preferably denote acrylate or methacrylate, furthermorefluoroacrylate. Sp^(a) and Sp^(b) in the compounds of the formula I andthe sub-formulae thereof preferably denote a radical selected from thegroup consisting of —(CH₂)_(p1)—, —(CH₂)_(p1)—O—, —(CH₂)_(p1)—O—CO— and—(CH₂)_(p1)—O—CO—O— and mirror images thereof, in which p1 denotes aninteger from 1 to 12, preferably from 1 to 6, particularly preferably 1,2 or 3, where these groups are linked to P^(a) or P^(b) in such a waythat O atoms are not directly adjacent.

Of the compounds of the formula P, particular preference is given tothose in which

-   -   the radicals P^(a) and P^(b) are selected from the group        consisting of vinyloxy, acrylate, methacrylate, fluoroacrylate,        chloroacrylate, oxetane and epoxide groups, particularly        preferably acrylate or methacrylate groups,    -   the radicals Sp^(a) and Sp^(b) are selected from the group        consisting of —(CH₂)_(p1)—, —(CH₂)_(p1)—O—, —(CH₂)_(p1)—O—CO—        and —(CH₂)_(p1)—O—CO—O— and mirror images thereof, in which p1        denotes an integer from 1 to 12, preferably from 1 to 6,        particularly preferably 1, 2 or 3, and where these radicals are        linked to P^(a) or P^(b) in such a way that O atoms are not        directly adjacent,

Compounds of formula P preferably used according to a preferredembodiment of the instant invention are those comprising exactly tworings (n1=n2=0), which are preferably 6-membered rings. Especiallypreferred are compounds selected from the group of compounds of thefollowing formulae:

wherein P^(a), P^(b), Sp^(a), Sp^(b), s1 and s2 are as defined underformula P above, and preferably Sp^(a/b) is alkylene —(CH₂)_(n)— whereinn preferably id 3, 4, 5, 6 or 7 and P^(a/b) a metacrylat- or acrylatemoiety. Especially preferred is the use of compounds selected from thegroup of formulae Pa, Pb, Pc, Pd, Pe, Pf, Pg, Ph and Pi and, inparticular the compounds of formula Pa.

The moiety “A²-Q¹-A³” preferably is a moiety of formula

wherein preferably at least one of the two phenylene rings issubstituted by at least one L, which is different from H, wherein r isindependently for each ring, and preferably it is for each ring 0, 1 or2.

For the compounds of formula P, as well as for its respectivesub-formulae, preferably

P^(a) and P^(b) are, independently from each other, acrylate ormethacrylate, but also fluoroacrylate,

Sp^(a) and Sp^(b) are, independently from each other, —(CH₂)_(p1)—,—(CH₂)_(p1)—O—, —O—(CH₂)_(p1)—, —(CH₂)_(p1)—O—CO—, —CO—O—(CH₂)_(p1)—,—(CH₂)_(p1)—O—CO—O— or —(CH₂)_(p1)—O—CO—O—, wherein p1 is an integerfrom 1 to 12, preferably from 1 to 6, particularly preferred 1, 2 or 3,and wherein these moieties are liked with P^(a) or P^(b) in such a waythat no O-atoms are linked directly to on another.

Especially preferred is the use of compounds of formula P, wherein

-   -   P^(a) and P^(b) are vinyleoxy-, acrylate-, methacrylata-,        fluoroacrylate-, chloroacrylate-, oxetane- or an epoxygroup,        particularly preferred acrylate- or methacrylate,    -   Sp^(a) and Sp^(b) are —(CH₂)_(p1)—, —(CH₂)_(p1)—O—,        —O—(CH₂)_(p1)—, —(CH₂)_(p1)—O—CO—, —CO—O—(CH₂)_(p1)—,        —(CH₂)_(p1)—O—CO—O— or —(CH₂)_(p1)—O—CO—O—, wherein p1 is an        integer from 1 to 12, preferably from 1 to 6, particularly        preferred 1, 2 or 3, and wherein these moieties are liked with        P^(a) or P^(b) in such a way that no O— atoms are linked        directly to on another.

For the production of polymer stabilised displays according to thepresent invention, the polymerisable compounds are polymerised orcrosslinked, in case one compound contains or more compounds contain twoor more polymerisable groups, by in-situ polymerisation in the LC mediumbetween the substrates of the LC display with application of a voltage.The polymerisation can be carried out in one step. It is also possiblefirstly to carry out the polymerisation with application of a voltage ina first step in order to generate a pretilt angle, and subsequently, ina second polymerisation step without an applied voltage, to polymeriseor crosslink the compounds which have not reacted in the first step(“end curing”).

Suitable and preferred polymerisation methods are, for example, thermalor photopolymerisation, preferably photopolymerisation, in particular UVphotopolymerisation. One or more initiators can optionally also be addedhere. Suitable conditions for the polymerisation and suitable types andamounts of initiators are known to the person skilled in the art and aredescribed in the literature. Suitable for free-radical polymerisationare, for example, the commercially available photoinitiatorsIrgacure651®, Irgacure184®, Irgacure907®, Irgacure369® or Darocure1173®(Ciba AG). If an initiator is employed, its proportion is preferably0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight.

The polymerisable compounds according to the invention are also suitablefor polymerisation without an initiator, which is accompanied byconsiderable advantages, such as, for example, lower material costs andin particular less contamination of the LC medium by possible residualamounts of the initiator or degradation products thereof. Thepolymerisation can thus also be carried out without the addition of aninitiator. In a preferred embodiment, the LC medium thus comprises nopolymerisation initiator.

The polymerisable component or the LC medium may also comprise one ormore stabilisers in order to prevent undesired spontaneouspolymerisation of the RMs, for example during storage or transport.Suitable types and amounts of stabilisers are known to the personskilled in the art and are described in the literature. Particularlysuitable are, for example, the commercially available stabilisers fromthe Irganox® series (Ciba AG), such as, for example, Irganox® 1076. Ifstabilisers are employed, their proportion, based on the total amount ofRMs or the polymerisable component, is preferably in the range from 10to 10,000 ppm, particularly preferably in the range from 50 to 500 ppm.

The polymerisable compounds of formula P used preferably according tothe present invention can be polymerised individually, but it is alsopossible to polymerise mixtures which comprise two or more polymerisablecompounds according to the invention, or mixtures comprising one or morepolymerisable compounds according to the invention and one or morefurther polymerisable compounds (comonomers), which are preferablymesogenic or liquid-crystalline. In the case of polymerisation of suchmixtures, copolymers form. A mixture of two or more compounds accordingto the invention or a mixture comprising one or more compounds accordingto the invention with one or more further polymerisable compounds ispreferably used. The invention furthermore relates to the polymerisablemixtures mentioned above and below. The polymerisable compounds andcomonomers are mesogenic or non-mesogenic, preferably mesogenic orliquid-crystalline.

Suitable and preferred co-monomers for use in polymer precursors forpolymer stabilised displays according to the invention are selected, forexample, from the following formulae:

wherein the parameters have the following meanings:

-   P¹ and P² each, independently of one another, a polymerisable group,    preferably having one of the meanings given above or below for    P^(a), particularly preferred an acrylate, methacrylate,    fluoroacrylate, oxetane, vinyloxy- or epoxy group,-   Sp¹ and Sp² each, independently of one another, a single bond or a    spacer group, preferably having one of the meanings given above or    below for Sp^(a), particularly preferred an —(CH₂)_(p1)—,    —(CH₂)_(p1)—O—, —(CH₂)_(p1)—CO—O— or —(CH₂)_(p1)—O—CO—O—, wherein p1    is an integer from 1 to 12, and wherein the groups mentioned last    are linked to the adjacent ring via the O-atom,-   and, wherein alternatively also one or more of P¹-Sp¹- and P²-Sp²-    may be R^(aa), provided that at least one of P¹-Sp¹- and P²-Sp²-    present in the compound is not R^(aa),-   R^(aa) H, F, Cl, CN or linear or branched alkyl having 1 to 25    C-atoms, wherein one or more non-adjacent —CH₂— groups,    independently of each another, may be replaced by —C(R⁰)═C(R⁰⁰)—,    —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a    way that neither O- nor S-atoms are directly linked to one another,    and wherein also one or more H-atoms may be replaced by F, Cl, CN or    P¹-Sp¹-, particularly preferred linear or branched, optionally    single- or polyfluorinated, alkyl, alkoxy, alkenyl, alkinyl,    alkylcarbonyl, alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12    C-atoms, wherein the alkenyl- and alkinyl groups have at least two    and the branched groups have at least three C-atoms,-   R⁰, R⁰⁰ each, at each occurrence independently of one another, H or    alkyl having 1 to 12 C-atoms,-   R^(y) and R^(z) each, independently of one another, H, F, CH₃ or    CF₃,-   Z¹ —O—, —CO—, —C(R^(y)R^(z))—, or —CF₂CF₂—,-   Z² and Z³ each, independently of one another, —CO—O—, —O—CO—,    —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, or —(CH₂)_(n)—, wherein n is 2, 3 or    4,-   L at each occurrence independently of one another, F, Cl, CN, SCN,    SF₅ or linear or branched, optionally mono- or polyfluorinated,    alkyl, alkoxy, alkenyl, alkinyl, alkylcarbonyl, alkoxycarbonyl,    alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C-atoms,    preferably F,-   L′ and L″ each, independently of one another, H, F or Cl,-   r 0, 1, 2, 3 or 4,-   s 0, 1, 2 or 3,-   t 0, 1 or 2, and-   x 0 or 1.

Suitable and preferred co-monomers for use in displays according to thepresent application operable and/or operating at a temperature where themesogenic medium is in the blue are for example selected from the groupof mono-reactive compounds, which are present in the precursor of thepolymer stabilised systems in a concentration in the range from 1 to 9wt.-%, particularly preferred from 4 to 7 wt.-%. Preferred mono-reactivecompounds are the compounds of formulae M1 bis M29, wherein one or moreof P¹-Sp¹- and P²-Sp²- are Rest R^(aa), such that the compounds have asingle reactive group only.

Particularly preferred mono-reactive compounds are the compounds of thefollowing formulae

wherein P¹, Sp¹ and R^(aa) have the respective meanings given above.

Amongst these the compounds of the formula

wherein

-   n is an integer, preferably an even integer, in the range from 1 to    16, preferably from 2 to 8,-   m is an integer in the range from 1 to 15, preferably from 2 to 7,    are especially preferred.

Particular preference is given to an LC medium, an LC display, a processor the use as described above and below in which the LC medium or thepolymerisable or polymerised component present therein comprises one ormore compounds of the following formula:

in which P^(a), P^(b), Sp^(a), Sp^(b), s1, s2 and L have the meaningsindicated above and below, r denotes 0, 1, 2, 3 or 4, and Z² and Z³each, independently of one another, denote —CF₂—O— or —O—CF₂—,preferably Z² is —CF₂—O— and Z³ is —O—CF₂— or vice versa, and, mostpreferably, Z² is —CF₂—O— and Z³ is —O—CF₂—.

The compounds of formula I are accessible by the usual methods known tothe expert. Starting materials may be, e.g., compounds of the followingtypes, which are either commercially available or accessible bypublished methods:

Preferably the liquid crystalline media according to the instantinvention contain a component A comprising, preferably predominantlyconsisting of and most preferably entirely consisting of compounds offormula I.

Comprising in this application means in the context of compositions thatthe entity referred to, e.g. the medium or the component, contains thecompound or compounds in question, preferably in a total concentrationof 10% or more and most preferably of 20% or more.

Predominantly consisting, in this context, means that the entityreferred to contains 80% or more, preferably 90% or more and mostpreferably 95% or more of the compound or compounds in question.

Entirely consisting, in this context, means that the entity referred tocontains 98% or more, preferably 99% or more and most preferably 100.0%of the compound or compounds in question.

The concentration of the compounds according to the present applicationare contained in the media according to the present applicationpreferably is in the range from 0.5% or more to 70% or less, morepreferably in the range from 1% or more to 60% or less and mostpreferably in the range from 5% or more to 50% or less.

In a preferred embodiment the mesogenic modulation media according tothe instant invention comprise

-   -   one compound or more compounds selected from the group of        compounds of formulae M-I and M-II, preferably in a total        concentration of 1% to 25% by weight, more preferably in a        concentration of 1% to 20% by weight, and most preferably        -   in a concentration of case of 1% to 10% by weight for each            single compound present, and/or    -   one compound or more compounds selected from the group of        compounds of formulae I and II, preferably in a concentration of        1% to 25% by weight, and/or    -   optionally, preferably obligatorily, one or more compounds        selected from the group of compounds of formulae IV and V and/or    -   of one or more chiral compounds with a HTP of ≧20 μm⁻¹,        preferably in a concentration of 1% to 20% by weight, and    -   optionally, preferably obligatorily, a polymer precursor,        comprising reactive compounds, preferably comprising reactive        mesogens, which, upon polymerisation, are able to, and        preferably do stabilize the phase range of the blue phase and/or        decrease the temperature dependence of the electro-optical        effect.

The inventive mixtures preferably comprise one or more compoundsselected from the group of compounds of formulae I and II and optionallyIII, preferably in a total concentration in the range from 40% or moreto 80% or less, preferably from 45% or more to 75% or less and mostpreferably from 50% or more to 70% or less.

In particular, the inventive mixtures preferably comprise one or morecompounds of formula I in a total concentration in the range from 40% ormore to 80% or less, preferably from 45% or more to 75% or less and mostpreferably from 50% or more to 70% or less.

In case the inventive mixtures comprise one or more compounds formulaII, the total concentration of these compounds preferably is in therange from 1% or more to 15% or less, preferably from 2% or more to 10%or less and most preferably from 4% or more to 8% or less.

In case the inventive mixtures comprise one or more compounds formulaIII, the total concentration of these compounds preferably is in therange from 1% or more to 20% or less, preferably from 2% or more to 15%or less and most preferably from 3% or more to 10% or less.

In case the inventive mixtures comprise one or more compounds formula IVthe total concentration of these compounds preferably is in the rangefrom 1% or more to 15% or less, preferably from 2% or more to 10% orless and, most preferably, from 4% or more to 8% or less.

In case the inventive mixtures comprise one or more compounds formula Vthe total concentration of these compounds preferably is in the rangefrom 5% or more to 45% or less, preferably from 15% or more to 40% orless and most preferably from 25% or more to 35% or less.

Suitable chiral compounds are those, which have an absolute value of thehelical twisting power of 20 μm⁻¹ or more, preferably of 40 μm⁻¹ or moreand most preferably of 60 μm⁻¹ or more. The HTP is measured in theliquid crystalline medium MLC-6260 at a temperature of 20° C.

The mesogenic media according to the present invention comprisepreferably one or more chiral compounds which have a mesogenic structureand exhibit preferably one or more meso-phases themselves, particularlyat least one cholesteric phase. Preferred chiral compounds beingcomprised in the mesogenic media are, amongst others, well known chiraldopants like cholesteryl-nonanoate (CN), R/S-811, R/S-1011, R/S-2011,R/S-3011, R/S-4011, R/S-5011, CB-15 (Merck KGaA, Darmstadt, Germany).Preferred are chiral dopants having one or more chiral moieties and oneor more mesogenic groups or having one or more aromatic or alicyclicmoieties forming, together with the chiral moiety, a mesogenic group.More preferred are chiral moieties and mesogenic chiral compoundsdisclosed in DE 34 25 503, DE 35 34 777, DE 35 34 778, DE 35 34 779, DE35 34 780, DE 43 42 280, EP 01 038 941 and DE 195 41 820 that disclosureis incorporated within this application by way of reference. Particularpreference is given to chiral binaphthyl derivatives as disclosed in EP01 111 954.2, chiral binaphthol derivatives as disclosed in WO 02/34739,chiral TADDOL derivatives as disclosed in WO 02/06265 as well as chiraldopants having at least one fluorinated linker and one end chiral moietyor one central chiral moiety as disclosed in WO 02/06196 and WO02/06195.

The mesogenic medium of the present invention has a characteristictemperature, preferably a clearing point, in the range from about −30°C. to about 90° C., especially up to about 70° C. or even 80° C.

The inventive mixtures preferably contain one ore more (two, three, fouror more) chiral compounds in the range of 1-25 wt. %, preferably 2-20wt. %, each. Especially preferred are mixtures containing 3-15 wt.-%total of one or more chiral compounds.

Preferred embodiments are indicated below:

-   -   The medium comprises one, two, three, four or more compounds of        formula I, preferably of formula I-2, and/or    -   the medium comprises one, two or more compounds of formula II,        preferably of formula II-3, and/or    -   the medium comprises one or more compounds of formula III and/or    -   the medium comprises one, two or more compounds of formula IV,        preferably of formula IV-2, and/or    -   the medium comprises one, two, three or more compounds of        formula V, and/or    -   the medium comprises one, two, three or more chiral compounds,        preferably having a helical twisting power of 20 μm⁻¹ or more,        and/or    -   the medium comprises one, two or more reactive compounds,        preferably one two or more reactive mesogenic compounds,        preferably of formulae P, preferably of one or more of its        sub-formulae, and/or one or more reactive mesogenic compounds        selected from the group of formulae M1 to M29, preferably of        formulae M16-A and/or M17-A, more preferably of formula M17-A′.

It has been found that even a relatively small proportion of compoundsof the formula I mixed with conventional liquid-crystal materials, butin particular with one or more compounds of the formulae II and III,leads to a lower operating voltage and a broader operating temperaturerange. Preference is given, in particular, to mixtures which, besidesone or more compounds of the formula I, comprise one or more compoundsof the formula III, in particular compounds of the formula III in whichR³ is n-butyl.

The compounds of the formulae I to V are colourless, stable and readilymiscible with one another and with other liquid-crystalline materials.

The optimum mixing ratio of the compounds of the formulae I and II andIII depends substantially on the desired properties, on the choice ofthe components of the formulae I, II and/or III, and on the choice ofany other components that may be present. Suitable mixing ratios withinthe range given above can easily be determined from case to case.

The total amount of compounds of the formulae I and II and optionallyIII in the mixtures according to the invention is in many cases notcrucial. The mixtures can therefore comprise one or more furthercomponents for the purposes of optimisation of various properties.However, the observed effect on the operating voltage and the operatingtemperature range is generally greater, the higher the totalconcentration of compounds of the formulae I and II and optionally III.

In a particularly preferred embodiment, the media according to theinvention comprise one or more compounds each of the formulae M-I and/orM-II and/or formulae I and II and optionally III. A favourablesynergistic effect with the compounds of the formula I results inparticularly advantageous properties. In particular, mixtures comprisingcompounds of formula I and of formula II and/or of formula III aredistinguished by their low operating voltages.

The individual compounds of the formulae M-I, M-II, I, II to III, IV andV, which can be used in the media according to the invention, are eitherknown or can be prepared analogously to the known compounds.

The construction of the MLC display according to the invention frompolarisers, electrode base plates and surface-treated electrodescorresponds to the conventional construction for displays of this type.The term conventional construction is broadly drawn here and also coversall derivatives and modifications of the MLC display, in particularincluding matrix display elements based on poly-Si TFT or MIM, however,particularly preferred are displays, which have electrodes on just oneof the substrates, i.e. so called inter-digital electrodes, as thoseused in IPS displays, preferably in one of the established structures.

A significant difference between the displays according to the inventionand the conventional displays based on the twisted nematic cellconsists, however, in the choice of the liquid-crystal parameters of theliquid-crystal layer.

The media according to the invention are prepared in a mannerconventional per se. In general, the components are dissolved in oneanother, advantageously at elevated temperature. By means of suitableadditives, the liquid-crystalline phases in accordance with theinvention can be modified in such a way that they can be used in alltypes of liquid crystal display elements that have been disclosedhitherto. Additives of this type are known to the person skilled in theart and are described in detail in the literature (H. Kelker and R.Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). Forexample, pleochroic dyes can be added for the preparation of colouredguest-host systems or substances can be added in order to modify thedielectric anisotropy, the viscosity and/or the alignment of the nematicphases. Furthermore, stabilisers and antioxidants can be added.

The mixtures according to the invention are suitable for TN, STN, ECBand IPS applications and isotropic switching mode (ISM) applications.Hence, there use in an electro-optical device and an electro-opticaldevice containing liquid crystal media comprising at least one compoundaccording to the invention are subject matters of the present invention.

The inventive mixtures are highly suitable for devices, which operate inan optically isotropic state. The mixtures of the invention aresurprisingly found to be highly suitable for the respective use.

Electro-optical devices that are operated or operable in an opticallyisotropic state recently have become of interest with respect to video,TV, and multi-media applications. This is, because conventional liquidcrystal displays utilizing electro-optical effects based on the physicalproperties of liquid crystals exhibit a rather high switching time,which is undesired for said applications. Furthermore most of theconventional displays show a significant viewing angle dependence ofcontrast that in turn makes necessary measures to compensate thisundesired property.

With regard to devices utilizing electro-optical effects in an isotropicstate the German Patent Application DE 102 17 273 A1 for examplediscloses light-controlling (light modulation) elements in which themesogenic controlling medium for modulation is in the isotropic phase atthe operating temperature. These light controlling elements have a veryshort switching time and a good viewing angle dependence of contrast.However, the driving or operating voltages of said elements are veryoften unsuitably high for some applications.

German Patent Application DE 102 41 301 yet unpublished describesspecific structures of electrodes allowing a significant reduction ofthe driving voltages. However, these electrodes make the process ofmanufacturing the light controlling elements more complicated.

Furthermore, the light controlling elements, for example, disclosed inboth DE 102 17 273 A1 and DE 102 41 301 show significant temperaturedependence. The electro-optical effect that can be induced by theelectrical field in the controlling medium being in an optical isotropicstate is most pronounced at temperatures close to the clearing point ofthe controlling medium. In this range the light controlling elementshave the lowest values of their characteristic voltages and, thus,require the lowest operating voltages. As temperature increases, thecharacteristic voltages and hence the operating voltages increaseremarkably. Typical values of the temperature dependence are in therange from about a few volts per centigrade up to about ten or morevolts per centigrade. While DE 102 41 301 describes various structuresof electrodes for devices operable or operated in the isotropic state,DE 102 17 273 A1 discloses isotropic media of varying composition thatare useful in light controlling elements operable or operated in theisotropic state. The relative temperature dependence of the thresholdvoltage in these light controlling elements is at a temperature of 1centigrade above the clearing point in the range of about50%/centigrade. That temperature dependence decreases with increasingtemperature so that it is at a temperature of 5 centigrade above theclearing point of about 10%/centigrade. However, for many practicalapplications of displays utilizing said light controlling elements thetemperature dependence of the electro-optical effect is too high. To thecontrary, for practical uses it is desired that the operating voltagesare independent from the operating temperature over a temperature rangeof at least some centi-grades, preferably of about 5 centi-grades ormore, even more preferably of about 10 centi-grades or more andespecially of about 20 centi-grades or more.

Now it has been found that the use of the inventive mixtures are highlysuitable as controlling media in the light controlling elements asdescribed above and in DE 102 17 273 A1, DE 102 41 301 and DE 102 536 06and broaden the temperature range in which the operating voltages ofsaid electro-optical operates. In this case the optical isotropic stateor the blue phase is almost completely or completely independent fromthe operating temperature.

This effect is even more distinct if the mesogenic controlling mediaexhibit at least one so-called “blue phase” as described in yetunpublished WO 2004/046 805. Liquid crystals having an extremely highchiral twist may have one or more optically isotropic phases. If theyhave a respective cholesteric pitch, these phases might appear bluish ina cell having a sufficiently large cell gap. Those phases are thereforealso called “blue phases” (Gray and Goodby, “Smectic Liquid Crystals,Textures and Structures”, Leonhard Hill, USA, Canada (1984)). Effects ofelectrical fields on liquid crystals existing in a blue phase aredescribed for instance in H. S. Kitzerow, “The Effect of Electric Fieldson Blue Phases”, Mol. Cryst. Liq. Cryst. (1991), Vol. 202, p. 51-83, aswell as the three types of blue phases identified so far, namely BP I,BP II, and BP III, that may be observed in field-free liquid crystals.It is noteworthy, that if the liquid crystal exhibiting a blue phase orblue phases is subjected to an electrical field, further blue phases orother phases different from the blue phases I, II and III might appear.

The inventive mixtures can be used in an electro-opticallight-controlling element which comprises

-   -   one or more, especially two substrates;    -   an assembly of electrodes;    -   one or more elements for polarizing the light; and    -   said controlling medium;        whereby said light-controlling element is operated (or operable)        at a temperature at which the controlling medium is in an        optically isotropic phase when it is in a non-driven state.

The controlling medium of the present invention has a characteristictemperature, preferably a clearing point, in the range from about −30°C. to about 90° C., especially up to about 70° C. to 80° C.

The operating temperature of the light controlling elements ispreferably above the characteristic temperature of the controllingmedium said temperature being usually the transition temperature of thecontrolling medium to the blue phase; generally the operatingtemperature is in the range of about 0.1° to about 50°, preferably inthe range of about 0.1° to about 10° above said characteristictemperature. It is highly preferred that the operating temperature is inthe range from the transition temperature of the controlling medium tothe blue phase up to the transition temperature of the controllingmedium to the isotropic phase which is the clearing point. The lightcontrolling elements, however, may also be operated at temperatures atwhich the controlling medium is in the isotropic phase.

(For the purposes of the present invention the term “characteristictemperature” is defined as follows:

-   -   If the characteristic voltage as a function of temperature has a        minimum, the temperature at this minimum is denoted as        characteristic temperature.    -   If the characteristic voltage as a function of temperature has        no minimum and if the controlling medium has one or more blue        phases, the transition temperature to the blue phase is denoted        as characteristic temperature; in case there are more than one        blue phase, the lowest transition temperature to a blue phase is        denoted as characteristic temperature.    -   If the characteristic voltage as a function of temperature has        no minimum, and if the controlling medium has no blue phase, the        transition temperature to the isotropic phase is denoted as        characteristic temperature.

In the context of the present invention the term “alkyl” means, as longas it is not defined in a different manner elsewhere in this descriptionor in the claims, straight-chain and branched hydrocarbon (aliphatic)radicals with 1 to 15 carbon atoms. The hydrocarbon radicals may beunsubstituted or substituted with one or more substituents beingindependently selected from the group consisting of F, Cl, Br, I or CN.

The dielectrics may also comprise further additives known to the personskilled in the art and described in the literature. For example, 0 to 5%of pleochroic dyes, antioxidants or stabilizers can be added.

C denotes a crystalline phase, S a smectic phase, S_(c) a smectic Cphase, N a nematic phase, I the isotropic phase and BP the blue phase.

V_(X) denotes the voltage for X % transmission. Thus e.g. V₁₀ denotesthe voltage for 10% transmission and V₁₀₀ denotes the voltage for 100%transmission (viewing angle perpendicular to the plate surface). t_(on)(respectively τ_(on)) denotes the switch-on time and t_(off)(respectively τ_(off)) the switch-off time at an operating voltagecorresponding the value of V₁₀₀, respectively of V_(max), t_(on) is thetime for the change of the relative transmission from 10% to 90% andt_(off) is the time for the change of the relative transmission from 90%to 10%. The response times are determined with the measurementinstrument DMS from Autronic Melchers, Germany, just as theelectro-optical characteristics.

Δn denotes the optical anisotropy. Δ∈ denotes the dielectric anisotropy(Δ∈=∈_(∥)-∈_(⊥), where ∈_(∥) denotes the dielectric constant parallel tothe longitudinal molecular axes and ∈_(∥) denotes the dielectricconstant perpendicular thereto). The electro-optical data are measuredin a TN cell at the 1^(st) minimum of transmission (i.e. at a (d·Δn)value of 0.5 μm) at 20° C., unless expressly stated otherwise. Theoptical data are measured at 20° C., unless expressly stated otherwise.

Optionally, the light modulation media according to the presentinvention can comprise further liquid crystal compounds in order toadjust the physical properties. Such compounds are known to the expert.Their concentration in the media according to the instant invention ispreferably 0% to 30%, more preferably 0% to 20% and most preferably 5%to 15%.

Preferably inventive media have a range of the blue phase or, in case ofthe occurrence of more than one blue phase, a combined range of the bluephases, with a width of 20° or more, preferably of 40° or more, morepreferably of 50° or more and most preferably of 60° or more.

In a preferred embodiment this phase range at least from 10° C. to 30°C., most preferably at least from 10° C. to 40° C. and most preferablyat least from 0° C. to 50° C., wherein at least means, that preferablythe phase extends to temperatures below the lower limit and at the sametime, that it extends to temperatures above the upper limit.

In another preferred embodiment this phase range at least from 20° C. to40° C., most preferably at least from 30° C. to 80° C. and mostpreferably at least from 30° C. to 90° C. This embodiment isparticularly suited for displays with a strong backlight, dissipatingenergy and thus heating the display.

Preferably the inventive media have a dielectric anisotropy of 150 ormore, more preferably of 200 or more, even more preferably of 250 ormore and most preferably of 300 or more. In particular, the value ofdielectric anisotropy of the inventive media is preferably 500 or less,more preferably 400 or less.

In the present application the term dielectrically positive compoundsdescribes compounds with Δ∈>1.5, dielectrically neutral compounds arecompounds with −1.5≦Δ∈≦1.5 and dielectrically negative compounds arecompounds with Δ∈<−1.5. The same holds for components. As is determinedat 1 kHz and 20° C. The dielectric anisotropies of the compounds isdetermined from the results of a solution of 10% of the individualcompounds in a nematic host mixture. The capacities of these testmixtures are determined both in a cell with homeotropic and withhomogeneous alignment. The cell gap of both types of cells isapproximately 20 μm. The voltage applied is a rectangular wave with afrequency of 1 kHz and a root mean square value typically of 0.5 V to1.0 V, however, it is always selected to be below the capacitivethreshold of the respective test mixture.

For dielectrically positive compounds the mixture ZLI-4792 and fordielectrically neutral, as well as for dielectrically negativecompounds, the mixture ZLI-3086, both of Merck KGaA, Germany are used ashost mixture, respectively. The dielectric permittivities of thecompounds are determined from the change of the respective values of thehost mixture upon addition of the compounds of interest and areextrapolated to a concentration of the compounds of interest of 100%.

Components having a nematic phase at the measurement temperature of 20°C. are measured as such, all others are treated like compounds.

The term threshold voltage refers in the instant application to theoptical threshold and is given for 10% relative contrast (V₁₀) and theterm saturation voltage refers to the optical saturation and is givenfor 90% relative contrast (V₉₀) both, if not explicitly statedotherwise. The capacitive threshold voltage (V₀, also calledFreedericksz-threshold V_(Fr)) is only used if explicitly mentioned.

The ranges of parameters given in this application are all including thelimiting values, unless explicitly stated otherwise.

Throughout this application, unless explicitly stated otherwise, allconcentrations are given in mass percent and relate to the respectivecomplete mixture, all temperatures are given in degrees centigrade(Celsius) and all differences of temperatures in degrees centigrade. Allphysical properties have been and are determined according to “MerckLiquid Crystals, Physical Properties of Liquid Crystals”, StatusNovember 1997, Merck KGaA, Germany and are given for a temperature of20° C., unless explicitly stated otherwise. The optical anisotropy (Δn)is determined at a wavelength of 589.3 nm. The dielectric anisotropy(Δ∈) is determined at a frequency of 1 kHz. The threshold voltages, aswell as all other electro-optical properties have been determined withtest cells prepared at Merck KGaA, Germany. The test cells for thedetermination of Δ∈ had a cell gap of 22 μm. The electrode was acircular ITO electrode with an area of 1.13 cm² and a guard ring. Theorientation layers were lecithin for homeotropic orientation (∈_(∥)) andpolyimide AL-1054 from Japan Synthetic Rubber for homogenous orientation(∈_(⊥)). The capacities were determined with a frequency responseanalyser Solatron 1260 using a sine wave with a voltage of 0.3 or 0.1V_(rms). The light used in the electro-optical measurements was whitelight. The set up used was a commercially available equipment of Otsuka,Japan. The characteristic voltages have been determined underperpendicular observation. The threshold voltage (V₁₀), mid-grey voltage(V₅₀) and saturation voltage (V₉₀) have been determined for 10%, 50% and90% relative contrast, respectively.

The mesogenic modulation material has been filled into an electrooptical test cell prepared at the respective facility of Merck KGaA. Thetest cells had inter-digital electrodes on one substrate side. Theelectrode width was 10 μm, the distance between adjacent electrodes was10 μm and the cell gap was also 10 μm. This test cell has been evaluatedelectro-optically between crossed polarisers.

At low temperatures, the filled cells showed the typical texture of achiral nematic mixture, with an optical transmission between crossedpolarisers without applied voltage. Upon heating, at a first temperature(T₁) the mixtures turned optically isotropic, being dark between thecrossed polarisers. This indicated the transition from the chiralnematic phase to the blue phase at that temperature. Up to a secondtemperature (T₂) the cell showed an electro-optical effect under appliedvoltage, typically of some tens of volts, a certain voltage in thatrange leading to a maximum of the optical transmission. Typically at ahigher temperature the voltage needed for a visible electro-opticaleffect increased strongly, indicating the transition from the blue phaseto the isotropic phase at this second temperature (T₂).

The temperature range (ΔT(BP)), where the mixture can be usedelectro-optically in the blue phase most beneficially has beenidentified as ranging from T₁ to T₂. This temperature range (ΔT(BP)) isthe temperature range given in the examples of this application. Theelectro-optical displays can also be operated at temperatures beyondthis range, i.e. at temperatures above T₂, albeit only at significantlyincreased operation voltages.

The liquid crystal media according to the present invention can containfurther additives and chiral dopants in usual concentrations. The totalconcentration of these further constituents is in the range of 0% to10%, preferably 0.1% to 6%, based in the total mixture. Theconcentrations of the individual compounds used each are preferably inthe range of 0.1 to 3%. The concentration of these and of similaradditives is not taken into consideration for the values and ranges ofthe concentrations of the liquid crystal components and compounds of theliquid crystal media in this application.

The inventive liquid crystal media according to the present inventionconsist of several compounds, preferably of 3 to 30, more preferably of5 to 20 and most preferably of 6 to 14 compounds. These compounds aremixed in conventional way. As a rule, the required amount of thecompound used in the smaller amount is dissolved in the compound used inthe greater amount. In case the temperature is above the clearing pointof the compound used in the higher concentration, it is particularlyeasy to observe completion of the process of dissolution. It is,however, also possible to prepare the media by other conventional ways,e.g. using so called pre-mixtures, which can be e.g. homologous oreutectic mixtures of compounds or using so called multi-bottle-systems,the constituents of which are ready to use mixtures themselves.

By addition of suitable additives, the liquid crystal media according tothe instant invention can be modified in such a way, that they areusable in all known types of liquid crystal displays, either using theliquid crystal media as such, like TN-, TN-AMD, ECB-, VAN-AMD and inparticular in composite systems, like PDLD-, NCAP- and PN-LCDs andespecially in HPDLCs.

The melting point: T(K,N), T(K,S) or T(K,I), respectively, thetransition temperature from one smectic phase (S_(X)) to another smecticphase (S_(Y)): T(S_(X),S_(Y)), the transition temperature from thesmectic (S) to the nematic (N) phase: T(S,N), the clearing point: T(N,I), and the glass transition temperature: T_(g) of the liquidcrystals, as applicable, as well as any other temperature throughoutthis application, are given in degrees centi-grade (i.e. Celsius).

The compounds of the formula P and the sub-formulae thereof can beprepared analogously to the process known to the person skilled in theart and described in standard works of organic chemistry, such as, forexample, in Houben-Weyl, Methoden der organischen Chemie [Methods ofOrganic Chemistry], Thieme-Verlag, Stuttgart.

Particularly suitable and preferred processes for the preparation ofcompounds of the formula P and the sub-formulae thereof are shown by wayof example in the following schemes and preferably comprise one or moreof the steps described below.

The person skilled in the art will be able to modify the synthesis in asuitable manner and thus obtain further compounds according to theinvention. The particularly preferred compounds containing an alkoxyspacer or acrylates bonded directly to the ring are obtained, forexample, by reaction of phenol derivatives, such as, for example,compound 12, with the dithianylium salts 13. The compounds 14 formedinitially here are converted into the compounds 15. The hydroxyl groupcan subsequently be functionalised in a suitable manner, for example byesterification using methacrylic acid (cf. Scheme 1).

The compounds of formula P wherein the rings are linked by an —CF₂—O—group and the reactive groups are attached to the rings via an alkylenespacer group, which are used according to the present invention in aparticularly preferred embodiment, can be prepared according to thefollowing scheme.

In the present invention and especially in the following examples, thestructures of the mesogenic compounds are indicated by means ofabbreviations, also called acronyms. In these acronyms, the chemicalformulae are abbreviated as follows using Tables A to C below. Allgroups C_(n)H_(2n+1), C_(m)H_(2m+1) and C_(l)H_(2l+1) or C_(n)H_(2n−1),C_(m)H_(2m−1) and C_(l)H_(2l+1) denote straight-chain alkyl or alkenyl,preferably 1E-alkenyl, each having n, m and l C atoms respectively.Table A lists the codes used for the ring elements of the corestructures of the compounds, while Table B shows the linking groups.Table C gives the meanings of the codes for the left-hand or right-handend groups. The acronyms are composed of the codes for the ring elementswith optional linking groups, followed by a first hyphen and the codesfor the left-hand end group, and a second hyphen and the codes for theright-hand end group. Table D shows illustrative structures of compoundstogether with their respective abbreviations.

TABLE A Ring elements C

D

A

G

U

Y

M

N

Np

N3f

tH

tH2f

K

L

F

P

Dl

Al

Gl

Ul

Ml

Nl

dH

N3fl

tHl

tH2fl

Kl

Ll

Fl

TABLE B Linking groups E —CH₂CH₂— Z —CO—O— V —CH═CH— ZI —O—CO— X —CF═CH—O —CH₂—O— XI —CH═CF— OI —O—CH₂— B —CF═CF— Q —CF₂—O— T —C≡C— QI —O—CF₂— W—CF₂CF₂— T —C≡C—

TABLE C End groups Left-hand side Right-hand side Use alone -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO- C_(n)H_(2n+1)—O— -nO—O—C_(n)H_(2n+1) -V- CH₂═CH— -V —CH═CH₂ -nV- C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ -Vn- CH₂═CH—C_(n)H_(2n+1)— -Vn —CH═CH—C_(n)H_(2n+1)-nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) -N- N≡C— -N —C≡N -S- S═C═N— -S —N═C═S-F- F— -F —F -CL- Cl— -CL —Cl -M- CFH₂— -M —CFH₂ -D- CF₂H— -D —CF₂H -T-CF₃— -T —CF₃ -MO- CFH₂O— -OM —OCFH₂ -DO- CF₂HO— -OD —OCF₂H -TO- CF₃O—-OT —OCF₃ -OXF- CF₂═CH—O— -OXF —O—CH═CF₂ -A- H—C≡C— -A —C≡C—H -nA-C_(n)H_(2n+1)—C≡C— -An —C≡C—C_(n)H_(2n+1) -NA- N≡C—C≡C— -AN —C≡C—C≡N Usetogether with one another and/or with others - . . . A . . . - —C≡C— - .. . A . . . —C≡C— - . . . V . . . - CH═CH— - . . . V . . . —CH═CH— - . .. Z . . . - —CO—O— - . . . Z . . . —CO—O— - . . . ZI . . . - —O—CO— - .. . ZI . . . —O—CO— - . . . K . . . - —CO— - . . . K . . . —CO— - . . .W . . . - —CF═CF— - . . . W . . . —CF═CF— in which n and m each denoteintegers, and the three dots “. . .” are place-holders for otherabbreviations from this table.

The following table shows illustrative structures together with theirrespective abbreviations. These are shown in order to illustrate themeaning of the rules for the abbreviations. They furthermore representcompounds which are preferably used.

TABLE D Illustrative structures

  MGQU-n-F

  MGQU-n-T

  MGQU-n-N

  MUQU-n-F

  MUQU-n-T

  MUQU-n-N

  NGQU-n-F

  NGQU-n-T

  NGQU-n-N

  NUQU-n-F

  NUQU-n-T

  NUQU-n-N

  GGP-n-F

  GGP-n-CL

  PGlGl-n-F

  PGlGl-n-CL

  GGP-n-T

  PGU-n-T

  GGU-n-T

  DPGU-n-F

  PPGU-n-F

  DPGU-n-T

  PPGU-n-T

  PUQU-n-N

  GUQU-n-N

  GUUQU-n-N

  GUUQU-n-N

  GUQU-n-F

  PUQGU-n-F

  GUQGU-n-F

  PUQGU-n-T

  GUQGU-n-T in which n (, m and l) preferably, independently of oneanother, denote(s) an integer from 1 to 7, preferably from 2 to 6.

The following table, Table E, shows illustrative compounds which can beused as stabiliser in the mesogenic media according to the presentinvention.

TABLE E

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table E.

The following table, Table F, shows illustrative compounds which canpreferably be used as chiral dopants in the mesogenic media according tothe present invention.

TABLE F

  C 15

  CB 15

  CM 21

  CM 44

  CM 45

  CM 47

  CC

  CN

  R/S-811

  R/S-1011

  R/S-2011

  R/S-3011

  R/S-4011

  R/S-5011

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table F.

The mesogenic media according to the present application preferablycomprise two or more, preferably four or more, compounds selected fromthe group consisting of the compounds from the above tables.

The liquid-crystal media according to the present invention preferablycomprise

-   -   seven or more, preferably eight or more, compounds, preferably        compounds having three or more, preferably four or more,        different formulae, selected from the group of the compounds        from Table D.

EXAMPLES

The examples below illustrate the present invention without limiting itin any way.

However, the physical properties show the person skilled in the art whatproperties can be achieved and in what ranges they can be modified. Inparticular, the combination of the various properties which canpreferably be achieved is thus well defined for the person skilled inthe art.

Liquid-crystal mixtures having the composition and properties asindicated in the following tables are prepared and investigated.

The so-called “HTP” denotes the helical twisting power of an opticallyactive or chiral substance in an LC medium (in μm⁻¹). Unless indicatedotherwise, the HTP is measured in the commercially available nematic LChost mixture MLD-6260 (Merck KGaA) at a temperature of 20° C.

Synthesis Example 16-(4-{[4-(6-Acryloyloxyhexyl)phenoxy]-difluoromethyl}-3,5-difluorophenyl)hexylacrylate 1.1:5-Bromo-2-[(4-bromophenoxy)difluoromethyl]-1,3-difluorobenzene

92.0 g (0.200 mol) of2-(4-bromo-2,6-difluorophenyl)-5,6-dihydro-4H-1,3-dithiyn-1-yliumtriflate are initially introduced in 600 ml of dichloromethane, and asolution of 52.0 g (0.300 mol) of 4-bromophenol in 200 ml ofdichloromethane and 45 ml of triethylamine is added at −70° C. When theaddition is complete, the mixture is stirred at −70° C. for a further 1h, 160 ml (1.00 mol) of triethylamine trishydrofluoride are added, and asolution of 51.0 ml (0.996 mol) of bromine in 200 ml of dichloromethaneis subsequently added dropwise. After 1 h, the cooling is removed, and,after warming to −10° C., the batch is added to a solution of 310 ml of32 percent sodium hydroxide solution in 2 l of ice-water. The org. phaseis separated off and washed with water. The aqueous phase is extractedwith dichloromethane, and the combined org. phases are dried over sodiumsulfate. The solvent is removed in vacuo, and the residue is filteredthrough silica gel with heptane, giving5-bromo-2-[(4-bromophenoxy)-difluoromethyl]-1,3-difluorobenzene as ayellow oil.

¹⁹F-NMR (CDCl₃, 235 MHz)

δ=−63.1 ppm (t, J=26.7 Hz, 2F, —CF₂O—), −112 (dt, J=9.7 Hz, J=26.7 Hz,2F, Ar—F).

1.2:6-(4-{Difluoro[4-(6-hydroxyhex-1-ynyl)phenoxy]methyl}-3,5-difluorophenyl)hex-5-yn-1-ol

10.7 g (25.8 mmol) of5-bromo-2-[(4-bromophenoxy)difluoromethyl]-1,3-difluorobenzene and 8.00g (81.5 mmol) of hex-5-yn-1-ol are initially introduced in 11.3 ml oftriethylamine and 500 ml of toluene, 1.50 g (2 mmol) ofbis(triphenylphosphine)palladium(II) chloride and 0.700 g (3.68 mmol) ofcopper(I) iodide are added, and the mixture is heated under refluxovernight. The batch is subsequently added to water, neutralised using 2N hydrochloric acid and extracted three times with toluene. The combinedorg. phases are dried over sodium sulfate, the solvent is removed invacuo, and the residue is chromatographed on silica gel firstly withtoluene and then with toluene/ethyl acetate (4:1), giving6-(4-{difluoro[4-(6-hydroxyhex-1-ynyl)phenoxy]methyl}-3,5-difluorophenyl)hex-5-yn-1-olas a colourless solid.

1.3:6-(4-{Difluoro[4-(6-hydroxyhexyl)phenoxy]methyl}-3,5-difluorophenyl)hexan-1-ol

6-(4-{Difluoro[4-(6-hydroxyhex-1-ynyl)phenoxy]methyl}-3,5-difluorophenyl)-hex-5-yn-1-olis hydrogenated to completion on palladium/active carbon catalyst inTHF. The catalyst is filtered off, the solvent is removed in vacuo, andthe crude product is chromatographed on silica gel with toluene/ethylacetate (1:2), giving6-(4-{difluoro[4-(6-hydroxyhexyl)-phenoxy]methyl}-3,5-difluorophenyl)hexan-1-olas a colourless solid.

¹⁹F-NMR (CDCl₃, 235 MHz)

δ=−60.8 ppm (t, J=26.3 Hz, 2F, —CF₂O—), −112 (dt, J=10.0 Hz, J=26.3 Hz,2F, Ar—F).

1.4:6-(4-{[4-(6-Acryloyloxyhexyl)phenoxy]difluoromethyl}-3,5-difluoro-phenyl)hexylacrylate

17.0 g (37.2 mmol) of6-(4-{difluoro[4-(6-hydroxyhexyl)phenoxy]methyl}-3,5-difluorophenyl)hexan-1-ol,8.05 g (112 mmol) of acrylic acid and 0.5 g of DMAP are initiallyintroduced in 300 ml of dichloromethane, and a solution of 17.3 g (112mmol) of EDC in 75 ml of dichloromethane is added dropwise with icecooling. After 1 h, the cooling is removed, and the batch is left tostir overnight at room temp. The vast majority of the solvent is removedin vacuo, and the residue is chromatographed on silica gel withdichloromethane, giving6-(4-{[4-(6-acryloyloxyhexyl)phenoxy]difluoromethyl}-3,5-difluorophenyl)hexylacrylate as a colourless oil.

Phase behaviour: T_(g)−71° C. 13 l.

¹H-NMR (CDCl₃, 250 MHz)

δ=1.25-1.48 ppm (m, 8H, CH₂), 1.50-1.74 ppm (m, 8H, CH₂), 2.60 (m, 4H,2-Ar—CH₂—), 4.13 (t, J=6.7 Hz, 2H, —CH₂O—), 4.15 (t, J=6.7 Hz, 2H,—CH₂O—), 5.81 (dt, J=10.4 Hz, J=1.8 Hz, 2H, 2CHH═CH—COO—), 6.11 (m_(c),2H, 2CH₂═CH—COO—), 6.39 (2CHH═CH—COO—), 6.78 (d, J=10.0 Hz, 2H, Ar—H),7.15 (m_(c), 4H, Ar—H).

¹⁹F-NMR (CDCl₃, 235 MHz)

δ=−60.9 ppm (t, J=26.4 Hz, 2F, —CF₂O—), −112.0 (dt, J=26.4, J=10.0 Hz,2F, Ar—F).

Analogously the following reactive compounds are obtained

Phase behaviour: to be determined.

Phase behaviour: T_(g)−66° C. I.

Phase behaviour: T_(g)−69° C. I.

Phase behaviour: to be determined.

Phase behaviour: to be determined.

Phase behaviour: to be determined.

Phase behaviour: to be determined.

Phase behaviour: C 128° C. I.

Phase behaviour: T_(g) −59° C. N −28.5° C. I.

Example 1

The following liquid crystalline mixture M-1 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-1 CompositionCompound Conc./ No. Abbreviation mass-% Physical Properties  1 MUQU-3-T 10.0 T(N, I) = 61° C.  2 GUQU-4-F  5.0 ε_(⊥)(20°, 1 kHz) = 13.2  3GUQU-5-F  5.0 Δε(20°, 1 kHz) = 358  4 PUQGU-3-T  8.0  5 PUQGU-5-T  5.0 6 GUQGU-2-T  12.0  7 GUQGU-3-T  12.0  8 GUQGU-4-T  14.0  9 GUQGU-5-T 14.0 10 GUQU-3-N  5.0 11 GUUQU-3-N  10.0 Σ 100.0

3.8% of the chiral agent R-5011 are solved in the achiral liquid crystalmixture and the electro-optical response of resultant mixture in anIPS-type cell is investigated. The mixture is filled into an electrooptical test cell with inter-digital electrodes on one substrate side.The electrode width is 10 μm, the distance between adjacent electrodesis 10 μm and the cell gap is also 10 μm. This test cell is evaluatedelectro-optically between crossed polarisers.

Appropriate Concentrations

a) of the chiral dopant R-5011 (Merck KGaA, Germany),

b) of the reactive mesogen of the formula RM-C

andc) alternatively of one of the two reactive mesogenic compounds of theformulae RM-1

and RM-2

respectively, are added to the mixture of interest, here mixture M-1.The resultant mixture is introduced into test cells and heated to anappropriate temperature, at which the mixture is in the blue phase. Thenit is exposed to UV.

The mixtures are characterised as described below before thepolymerisation. The reactive components are then polymerised in the bluephase by irradiation once (180 s), and the resultant media arere-characterised.

Detailed Description of the Polymerisation

Before the polymerisation of a sample, the phase properties of themedium are established in a test cell having a thickness of about 10microns and an area of 2×2.5 cm². The filling is carried out bycapillary action at a temperature of 75° C. The measurement is carriedout under a polarising microscope with heating stage with a temperaturechange of 1° C./min.

The polymerisation of the media is carried out by irradiation with a UVlamp (Dymax, Bluewave 200, 365 nm interference filter) having aneffective power of about 3.0 mW/cm² for 180 seconds. The polymerisationis carried out directly in the electro-optical test cell.

The polymerisation is carried out initially at a temperature at whichthe medium is in the blue phase I (BP-I). The polymerisation is carriedout in a plurality of part-steps, which gradually result in completepolymerisation. The temperature range of the blue phase generallychanges during the polymerisation. The temperature is therefore adaptedbetween each part-step so that the medium is still in the blue phase. Inpractice, this can be carried out by observing the sample under thepolarising microscope after each irradiation operation of about 5 s orlonger. If the sample becomes darker, this indicates a transition intothe isotropic phase. The temperature for the next part-step is reducedcorrespondingly.

The entire irradiation time which results in maximum stabilisation istypically 180 s at the irradiation power indicated. Furtherpolymerisations can be carried out in accordance with an optimisedirradiation/temperature programme.

Alternatively, the polymerisation can also be carried out in a singleirradiation step, in particular if a broad blue phase is already presentbefore the polymerisation.

Electro-Optical Characterisation

After the above-described polymerisation and stabilisation of the bluephase, the phase width of the blue phase is determined. Theelectro-optical characterisation is carried out subsequently at varioustemperatures within and if desired also outside this range.

The test cells used are fitted on one side with interdigital electrodeson the cell surface. The cell gap, the electrode separation and theelectrode width are typically each 10 microns. This uniform dimension isreferred to below as the gap width. The area covered by electrodes isabout 0.4 cm². The test cells do not have an alignment layer.

For the electro-optical characterisation, the cell is located betweencrossed polarising filters, where the longitudinal direction of theelectrodes adopts an angle of 45° to the axes of the polarising filter.The measurement is carried out using a DMS301 (Autronic-Melchers,Germany) at a right angle to the cell plane, or by means of a highlysensitive camera on the polarising microscope. In the voltage-freestate, the arrangement described gives an essentially dark image(definition 0% transmission).

Firstly, the characteristic operating voltages and then the responsetimes are measured on the test cell. The operating voltage is applied tothe cell electrodes in the form of rectangular voltage having analternating sign (frequency 100 Hz) and variable amplitude, as describedbelow.

The transmission is measured while the operating voltage is increased.The attainment of the maximum value of the transmission defines thecharacteristic quantity of the operating voltage V₁₀₀. Equally, thecharacteristic voltage V₁₀ is determined at 10% of the maximumtransmission. These values are measured at various temperatures in therange of the blue phase.

Relatively high characteristic operating voltages V₁₀₀ are observed atthe upper and lower end of the temperature range of the blue phase. Inthe region of the minimum operating voltage, V₁₀₀ generally onlyincreases slightly with increasing temperature. This temperature range,limited by T₁ and T₂, is referred to as the usable, flat temperaturerange (FR). The width of this “flat range” (FR) is (T₂-T₁) and is knownas the width of the flat range (WFR). The precise values of T₁ and T₂are determined by the intersections of tangents on the flat curvesection FR and the adjacent steep curve sections in the V₁₀₀/temperaturediagram.

In the second part of the measurement, the response times duringswitching on and off (τ_(on), τ_(off)) are determined. The response timeτ_(on) is defined by the time to achievement of 90% intensity afterapplication of a voltage at the level of V₁₀₀ at the selectedtemperature. The response time τ_(off) is defined by the time until thedecrease by 90% starting from maximum intensity at V₁₀₀ after reductionof the voltage to 0 V. The response time is also determined at varioustemperatures in the range of the blue phase.

As further characterisation, the transmission at continuously increasingand falling operating voltage between 0 V and V₁₀₀ is measured at atemperature within the FR. The difference between the two curves isknown as hysteresis. The difference in the transmissions at 0.5·V₁₀₀ andthe difference in the voltages at 50% transmission are, for example,characteristic hysteresis values and are known as ΔT₅₀ and ΔV₅₀respectively.

As a further characteristic quantity, the ratio of the transmission inthe voltage-free state before and after passing through a switchingcycle can be measured. This transmission ratio is referred to as the“memory effect”. The value of the memory effect is 1.0 in the idealstate. Values above 1 mean that a certain memory effect is present inthe form of excessively high residual transmission after the cell hasbeen switched on and off. This value is also determined in the workingrange of the blue phase (FR).

Typical concentrations of the polymer precursors are as follows.

Sample Constituent 1 2 3 Concentration/% M-1  87.0  89.0  87.4 R-5011 3.8  3.8  3.4 RM-C  5.0  4.0  5.0 RM-2  4.0  3.0  4.0 IRG-651 ®  0.2 0.2  0.2 Σ 100.0 100.0 100.0

The polymerisable mixture is polymerised in a single irradiation step ata temperature of about 30-50° C. at the lower end of the temperaturerange of the blue phase. The polymer-stabilised liquid-crystalline mediaexhibit a blue phase over a broad temperature range.

The polymer-stabilised medium M-1, prepared using the monomer (1)according to the invention, exhibits a reduction in hysteresis (ΔV₅₀)and good contrast on switching on and on switching off compared withconventional media from the prior art. In particular, the contrast onswitching on and the contrast on switching off are close together in themedium M1 according to the invention, which means very goodstabilisation of the blue phase.

It can be seen from this that the monomers according to the inventionare particularly suitable for the stabilisation of blue phases, inparticular in the case of media having a high concentration of chiraldopant.

Comparative Examples 1-1 and 1-2

The following liquid crystalline mixture (C-1) is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture C-1 CompositionCompound Conc./ No. Abbreviation mass-% Physical Properties  1 AUUQU-2-F 10.0 T(N, I) = 71° C.  2 AUUQU-3-F  11.0 Δn(20° C., 589 nm) = 0.1515  3AUUQU-4-F  7.0 Δε(20°, 1 kHz) = 224  4 AUUQU-5-F  6.0 γ₁(30° C.) = 763mPa · s  5 AUUQU-7-F  7.0  6 AUUQU-3-T  10.0  7 AUUQU-3-OT  11.0  8AGUQU-3-F  4.0  9 AUUQU-3-N  5.0 10 PUZU-2-F  7.0 11 PUZU-3-F  11.0 12PUZU-5-F  11.0 Σ 100.0

This mixture is treated and investigated as described in detail underexample 1 above. The results are compiled in the following table.

Mixture C-1-1 C-1-2 Host C-1 Reactive mesogen RM-1 RM-2 Measurementvalues (20° C.) Transition point before the t.b.d. t.b.d. polymerisationPolymerisation temperature/° C. t.b.d t.b.d V₁₀ (20° C.)/V  29.8.   20.8V₉₀ (20° C.)/V   58.6   42.0 V₁₀₀ (20° C.)/V   67.0   47.9 ΔV₅₀ (20°C.)/V    4.73    1.90 Contrast, switching on 285 206 Contrast, switchingoff 276 208 Memory effect    1.04    0.99 Remarks: t.b.d.: to bedetermined

Comparative Example 2

The following liquid crystalline mixture (C-2) is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture C-2 CompositionCompound Conc./ No. Abbreviation mass-% Physical Properties  1 GUQU-3-F 5.0 T (N, I) = 65° C.  2 GUQU-4-F  6.0 n_(e) (20° C., 589 nm) = 1.6690 3 GUQU-5-F  6.0 Δn(20° C., 589 nm) = 0.1859  4 PUQGU-3-T  8.0ε_(⊥)(20°, 1 kHz) = 12.9  5 PUQGU-5-T  8.0 Δε(20°, 1 kHz) = 277.8  6GUQGU-2-T  12.0  7 GUQGU-3-T  12.0  8 GUQGU-4-T  14.0  9 GUQGU-5-T  14.010 GUQU-3-N  5.0 11 GUUQU-3-N  10.0 Σ 100.0

Mixture CM-2-1 CM-2-2 Host C-2 Reactive mesogen RM-1 RM-2 Measurementvalues (20° C.) Transition point before the t.b.d. t.b.d. polymerisationPolymerisation temperature/° C. t.b.d. t.b.d. V₁₀ (20° C.)/V t.b.d. 19.5 V₉₀ (20° C.)/V t.b.d.  38.2 V₁₀₀ (20° C.)/V t.b.d.  43.0 ΔV₅₀ (20°C.)/V t.b.d.   2.16 Contrast, switching on t.b.d. t.b.d. Contrast,switching off t.b.d. t.b.d. Memory effect t.b.d.   1.03 V₁₀₀ (30° C.)/Vt.b.d.  52.0 t_(on) (30° C.)/ms t.b.d.  2.0 t_(off) (30° C.)/ms t.b.d. 1.6 Contrast, switching on t.b.d. 159.5 Contrast, switching off t.b.d.144.4 Memory effect t.b.d.   1.10 Remarks: t.b.d.: to be determined

Example 2

The following liquid crystalline mixture M-2 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-2 CompositionCompound Conc./ No. Abbreviation mass-% Physical Properties  1 MUQU-3-F 10.0 T (N, I) = 58° C.  2 GUQU-4-F  6.0 n_(e) (20° C., 589 nm) = 1.6689 3 GUQU-5-F  6.0 Δn(20° C., 589 nm) = 0.1843  4 PUQGU-3-T  5.0ε_(⊥)(20°, 1 kHz) = 13.6  5 PUQGU-5-T  6.0 Δε(20°, 1 kHz) = 253  6GUQGU-2-T  12.0  7 GUQGU-3-T  12.0  8 GUQGU-4-T  14.0  9 GUQGU-5-T  14.010 GUQU-3-N  5.0 11 GUUQU-3-N  10.0 Σ 100.0 Remarks: t.b.d.: to bedetermined

Typical concentrations of the polymer precursors are as follows.

Sample 1 Constituent Concentration % M-2 88  R-5011  3.8 RM-C  5.0 RM-1 0.0 RM-2  3.0 IRG-651 ®  0.2 Σ 100.0

The results are summarised in the following table.

Mixture M-2-1 Host M-2 Reactive mesogen RM-1 Measurement values (20° C.)Transition point before the 28.9 polymerisation Polymerisationtemperature/° C. 29.4 V₁₀ (20° C.)/V 22.2 V₉₀ (20° C.)/V 42.2 ΔV₅₀ (20°C.)/V 208   Contrast, switching on 203   Contrast, switching off 203  Memory effect  1.0

Example 3

The following liquid crystalline mixture M-3 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-3 CompositionCompound Conc./ No. Abbreviation mass-% Physical Properties  1 MUQU-3-F 20.0 T (N, I) = 49° C.  2 GUQU-4-F  4.0 n_(e) (20° C., 589 nm) = 1.6624 3 GUQU-5-F  4.0 Δn(20° C., 589 nm) = 0.1755  4 PUQGU-3-T  8.0ε_(⊥)(20°, 1 kHz) = 14.6  5 PUQGU-5-T  8.0 Δε(20°, 1 kHz) = 211  6GUQGU-2-T  11.0  7 GUQGU-3-T  10.0  8 GUQGU-4-T  10.0  9 GUQGU-5-T  10.010 GUQU-3-N  5.0 11 GUUQU-3-N  10.0 Σ 100.0

Example 4

The following liquid crystalline mixture M-4 is prepared andinvestigated with respect to its general physical properties. Thecomposition and properties are given in the following table.

Composition and properties liquid crystal mixture M-5 CompositionCompound Conc./ No. Abbreviation mass-% Physical Properties  1 MQU-3-F 10.0 T (N, I) = 67° C.  2 GUQU-3-F  4.0 ε_(⊥)(20°, 1 kHz) = 11.4  3GUQU-5-F  2.0 Δε(20°, 1 kHz) = 275  4 PUQGU-3-T  11.0  5 PUQGU-4-T  10.0 6 PUQGU-5-T  10.0  7 GUQGU-2-T  10.0  8 GUQGU-3-T  10.0  9 GUQGU-4-T 9.0 10 GUQGU-5-T  9.0 11 GUQU-3-N  5.0 12 GUUQU-3-N  10.0 Σ 100.0Remarks: t.b.d.: to be determined

Typical concentrations of the polymer precursors are as follows.

Sample 1 Constituent Concentration/% M-2  88.0 R-5011  3.8 RM-C  5.0RM-1  0.0 RM-2  3.0 IRG-651 ®  0.2 Σ 100.0

The results are summarised in the following table.

Mixture M-5-1 Host M-5 Reactive mesogen RM-1 Measurement values (20° C.)Transition point before the 37   polymerisation Polymerisationtemperature/° C. 37.5 V₁₀ (20° C.)/V 19.4 V₉₀ (20° C.)/V 38.3 V₁₀₀ (20°C.)/V 43.2 ΔV₅₀ (20° C.)/V  1.67 V₁₀₀ (30° C.)/V 54.0 t_(on) (30° C.)/ms 2.3 t_(off) (30° C.)/ms  1.7 Contrast, switching on 122.1  Contrast,switching off 121.7  Memory effect  1.00 Remarks: t.b.d.: to bedetermined

The invention claimed is:
 1. A mesogenic medium exhibiting a blue phase,comprising one or more compounds of formula M-I or M-II

and one or more compounds of formula I

wherein R⁰* is F, CF₃ or CN, L⁰ is F, R⁰ is alkyl, which is straightchain or branched, is unsubstituted, mono- or poly-substituted by F, Clor CN, and in which one or more CH₂ groups are optionally replaced, ineach case independently from one another, by —O—, —S—, —NR⁰¹—,—SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or—C≡C— in such a manner that O and/or S atoms are not linked directly toone another, Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN,and alternatively one of them may be H, R⁰¹ and R⁰² are, independentlyof each other, H or alkyl with 1 to 12 C-atoms L¹ is H or F, and R¹ isalkyl, which is straight chain or branched, is unsubstituted, mono- orpoly-substituted by F, Cl or CN, and in which one or more CH₂ groups areoptionally replaced, in each case independently from one another, by—O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—,—CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such a manner that O and/or S atoms arenot linked directly to one another.
 2. The mesogenic medium according toclaim 1, further comprising one or more compounds of formula II

wherein R²* is F or CF₃, L²¹ to L²³ are, independently of each other, Hor F, R² is alkyl, which is straight chain or branched, isunsubstituted, mono- or poly-substituted by F, Cl or CN, and in whichone or more CH₂ groups are optionally replaced, in each caseindependently from one another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—,—COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such amanner that O and/or S atoms are not linked directly to one another, Y⁰¹and Y⁰² are, independently of each other, F, Cl or CN, and alternativelyone of them may be H, and R⁰¹ and R⁰² are, independently of each other,H or alkyl with 1 to 12 C-atoms.
 3. The mesogenic medium according toclaim 1, which comprises one or more polymerizable compounds.
 4. Themesogenic medium according to claim 1, further comprising one or morecompounds of formula III

wherein R²* is F or CF₃, R³ is straight chain or branched, isunsubstituted, mono- or poly-substituted by F, Cl or CN, and in whichone or more CH₂ groups are optionally replaced, in each caseindependently from one another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—,—COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such amanner that O and/or S atoms are not linked directly to one another, Y⁰¹and Y⁰² are, independently of each other, F, Cl or CN, and alternativelyone of them may be H, and R⁰¹ and R⁰² are, independently of each other,H or alkyl with 1 to 12 C-atoms.
 5. The mesogenic medium according toclaim 1, further comprising one or more compounds of formula IV or V

wherein R⁴ and R⁵ are, independently of each other, alkyl, which isstraight chain or branched, is unsubstituted, mono- or poly-substitutedby F, Cl or CN, and in which one or more CH₂ groups are optionallyreplaced, in each case independently from one another, by —O—, —S—,—CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a mannerthat O and/or S atoms are not linked directly to one another, L⁵ is H orF,

n and m are, independently of one another, 0 or
 1. 6. The mesogenicmedium according to claim 1, which comprises one or more compounds offormula M-I.
 7. A mesogenic medium exhibiting a blue phase, comprisingone or more compounds of formula M-II

wherein R⁰* is F, CF₃ or CN, L⁰ is F, R⁰ is alkyl, which is straightchain or branched, is unsubstituted, mono- or poly-substituted by F, Clor CN, and in which one or more CH₂ groups are optionally replaced, ineach case independently from one another, by —O—, —S—, —NR⁰¹—,—SiR⁰¹R⁰²—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or—C≡C— in such a manner that O and/or S atoms are not linked directly toone another, Y⁰¹ and Y⁰² are, independently of each other, F, Cl or CN,and alternatively one of them may be H, and R⁰¹ and R⁰² are,independently of each other, H or alkyl with 1 to 12 C-atoms.
 8. Amethod for stabilizing the mesogenic medium according to claim 3,comprising polymerizing the polymerizable compounds in said medium. 9.The mesogenic medium according to claim 3, which has been stabilized bythe polymerization of the polymerizable compounds in said medium.
 10. Alight modulation element, comprising a medium according to claim
 1. 11.An electro-optical display, comprising a medium according to claim 1.12. The mesogenic medium according to claim 6, wherein R⁰* is CF₃ or CN.13. The mesogenic medium according to claim 1, further comprising one ormore compounds of formula PP^(a)-(Sp^(a))_(s1)-(A¹-Z¹)_(n1)-A²-Q-A³-(Z⁴-A⁴)_(n2)-(Sp^(b))_(s2)-P^(b)  Pwherein P^(a), P^(b) each, independently of one another, are apolymerisable group, Sp^(a), Sp^(b) each, independently of one another,denote a spacer group, s1, s2 each, independently of one another, denote0 or 1, n1, n2 each, independently of one another, denote 0 or 1,preferably 0, Q¹ denotes —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —(CO)O—,—O(CO)—, —(CH₂)₄—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—, —CH₂—CF₂—, —CH═CH—,—CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CF—, —C≡C—, —O—, —CH₂—,—(CH₂)₃—, —CF₂—, Z¹, Z⁴ denote a single bond, —CF₂O—, —OCF₂—, —CH₂O—,—OCH₂—, —(CO)O—, —O(CO)—, —(CH₂)₄—, —CH₂CH₂—, —CF₂—CF₂—, —CF₂—CH₂—,—CH₂—CF₂—, —CH═CH—, —CF═CF—, —CF═CH—, —(CH₂)₃O—, —O(CH₂)₃, —CH═CF—,—C≡C—, —O—, —CH₂—, —(CH₂)₃—, —CF₂—, where Z¹ and Q¹ or Z² and Q¹ do notsimultaneously denote a group selected from —CF₂O— and —OCF₂—, A¹, A²,A³, A⁴ each, independently of one another, denote a)trans-1,4-cyclohexylene, 1,4-cyclohexenylene or 1,4′-bicyclohexylene, inwhich one or more non-adjacent CH₂ groups are replaced by —O— and/or —S—and in which one or more H atoms are optionally replaced by F, b)1,4-phenylene or 1,3-phenylene, in which one or two CH groups areoptionally replaced by N and in which one or more H atoms are optionallyreplaced by L, c) tetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl,tetrahydrofuran-2,5-diyl, cyclobutane-1,3-diyl, piperidine-1,4-diyl,thiophene-2,5-diyl or selenophene-2,5-diyl, each of which is optionallymono- or polysubstituted by L, or d) a saturated, partially unsaturatedor fully unsaturated, and optionally substituted, polycyclic radicalshaving 5 to 20 cyclic C atoms, one or more of which may, in addition, bereplaced by heteroatoms.
 14. The mesogenic medium according to claim 13,wherein A¹, A², A³, A⁴ each, independently of one another, denote a)trans-1,4-cyclohexylene, 1,4-cyclohexenylene or 1,4′-bicyclohexylene, inwhich one or more non-adjacent CH₂ groups are replaced by —O— and/or —S—and in which one or more H atoms are optionally replaced by F, b)1,4-phenylene or 1,3-phenylene, in which one or two CH groups areoptionally replaced by N and in which one or more H atoms are optionallyreplaced by L, c) tetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl,tetrahydrofuran-2,5-diyl, cyclobutane-1,3-diyl, piperidine-1,4-diyl,thiophene-2,5-diyl or selenophene-2,5-diyl, each of which is optionallymono- or polysubstituted by L, or d) bicyclo[1.1.1]pentane-1,3-diyl,bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl,

wherein one or more H atoms are optionally replaced by L, and/or one ormore double bonds are optionally replaced by single bonds, and/or one ormore CH groups are optionally replaced by N, L on each occurrence,identically or differently, denotes F, Cl, CN, SCN, SF₅ orstraight-chain or branched, in each case optionally fluorinated, alkyl,alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy oralkoxycarbonyloxy having 1 to 12 C atoms, R⁰, R⁰⁰ each, independently ofone another, denote H, F or straight-chain or branched alkyl having 1 to12 C atoms, in which one or more H atoms are optionally replaced by F, Mdenotes —O—, —S—, —CH₂—, —CHY¹— or —CY¹Y²—, and Y¹ and Y² each,independently of one another, have one of the meanings indicated abovefor R⁰, or denote Cl or CN, and one of the groups Y¹ and Y²alternatively denotes —OCF₃.
 15. The mesogenic medium according to claim13, which has been stabilized by the polymerization of one or morecompounds of formula P.
 16. The mesogenic medium according to claim 13,further comprising one or more compounds of formula II

wherein R²* is F or CF₃, L²¹ to L²³ are, independently of each other, Hor F, R² is alkyl, which is straight chain or branched, isunsubstituted, mono- or poly-substituted by F, Cl or CN, and in whichone or more CH₂ groups are optionally replaced, in each caseindependently from one another, by —O—, —S—, —NR⁰¹—, —SiR⁰¹R⁰²—, —CO—,—COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such amanner that O and/or S atoms are not linked directly to one another, Y⁰¹and Y⁰² are, independently of each other, F, Cl or CN, and alternativelyone of them may be H, and R⁰¹ and R⁰² are, independently of each other,H or alkyl with 1 to 12 C-atoms.
 17. The mesogenic medium according toclaim 13, further comprising one or more compounds of formula III

wherein R²* is F or CF₃, R³ is straight chain or branched, isunsubstituted, mono- or poly-substituted by F, Cl or CN, and in whichone or more CH₂ groups are optionally replaced, in each caseindependently from one another, by —O—, —S—, —NR⁰¹, —SiR⁰¹R⁰²—, —CO—,—COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CY⁰¹═CY⁰²— or —C≡C— in such amanner that O and/or S atoms are not linked directly to one another, Y⁰¹and Y⁰² are, independently of each other, F, Cl or CN, and alternativelyone of them may be H, and R⁰¹ and R⁰² are, independently of each other,H or alkyl with 1 to 12 C-atoms.
 18. The mesogenic medium according toclaim 13, further comprising one or more compounds of formula IV or V

wherein R⁴ and R⁵ are, independently of each other, alkyl, which isstraight chain or branched, is unsubstituted, mono- or poly-substitutedby F, Cl or CN, and in which one or more CH₂ groups are optionallyreplaced, in each case independently from one another, by —O—, —S—,—CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— in such a mannerthat O and/or S atoms are not linked directly to one another, L⁵ is H orF,

n and m are, independently of one another, 0 or
 1. 19. The mesogenicmedium according to claim 13, which comprises one or more compounds offormula M-I.
 20. The mesogenic medium according to claim 13, whichcomprises one or more compounds of formula M-II.
 21. The mesogenicmedium according to claim 1, wherein the one or more compounds offormula I are present in a total concentration in the range from 40% ormore to 80% or less.